TMDS171 Datasheet, PDF (24/62 Pages) Texas Instruments – 3.4 Gbps TMDS RETIMER

TMDS171, TMDS171I
SLLSEN7A – OCTOBER 2015 – REVISED DECEMBER 2015
www.ti.com
Figure 26. Adaptive EQ Gain Curve
8.3.7 Input Signal Detect Block
When SIG_EN is enabled, the TMDS looks for a valid TMDS clock signal input. The terminations on the TMDS
data lines are connected and the device is fully functional when a valid signal is detected. If no valid TMDS clock
signal is detected, the device enters standby mode waiting for a valid signal at the clock input. The internal CDR
is shut down and all of the TMDS outputs and IN_D[0:2] are in high-Z status. TMDS signal detect circuit can be
set as enable by SIG_EN pin or through local I²C control but is default disabled. For HDMI compliance testing
(TMDS termination-voltage test), the clock-detect feature should be in disable status, default configuration.
Designers are recommended to activate this function in normal operation for power saving.
8.3.8 Audio Return Channel
The Audio Return Channel in TMDS171 enables a TV, via a single HDMI cable, to send audio data “upstream” to
an A/V receiver or surround audio controller, increasing user flexibility and eliminating the need for any separate
S/PDIF audio connection. The TMDS171 supports single mode audio return channel. Implementers can send the
S/PDIF signal to SPDIF_IN. The signal from ARC_OUT is sent to HDMI connectors and is passed through the
general HDMI cable to audio receiver. By I²C control, customer can disable ARC_OUT by register. Enabled by
default after initialization.
8.3.9 Transmitter Impedance Control
Source termination is disabled at data rates < 2 Gbps. When the data rate is between 2 Gbps and 3.4 Gbps, the
output signal may be better if the termination value around 150 Ω to 300 Ω depending upon system
implementation. TMDS171 supports two different source termination impedances for ease of implementation. Pin
36, TX_TERM_CTL, offers a selection option to choose the output termination impedance value.
Control Pin 36
TX_TERM_CTL = H
TX_TERM_CTL = L
TX_TERM_CTL = Z
Table 3. TX Termination Control
DESCRIPTION
The transmit Termination is disabled
The transmit Termination is set between 150 Ω ≈ 300 Ω
Automatic select the impedance
• 2 Gbps > DR < 3.4 Gbps – 150 - 300 Ω differential near end termination
• DR < 2 Gbps – no termination
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